Disintegrating ball for sealing frac plug seat

ABSTRACT

A composition for a ball that disintegrates, dissolves, delaminates or otherwise experiences a significant degradation of its physical properties over time in the presence of hydrocarbons and formation heat. The ball may be used in methods and apparatus for hydraulically fracturing a subterranean zone in a wellbore.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of the filing date of (i) U.S.Provisional Application No. 61/433,011 filed on Jan. 14, 2011 andentitled “Disintegrating Ball for Sealing Frac Plug Seat,” and (ii) U.S.Provisional Application No. 61/540,353 filed on Sep. 28, 2011 andentitled “Disintegrating Ball for Sealing Frac Plug Seat,” suchprovisional applications being hereby incorporated herein by referencein their entirety.

FIELD OF THE INVENTION

The present invention relates to a ball used in well stimulation tocreate a seal when dropped down a wellbore onto a frac plug seat. Morespecifically, it relates to a ball that has sufficient rigidity toresist deformation and withstand the high pressure differentials,typically up to 10,000 psi, that are required during well stimulation,but is capable of disintegrating, dissolving, delaminating or otherwiseexperiencing a significant degradation of its physical properties in thepresence of hydrocarbons and latent heat following well stimulation.Extraction from the hole or milling the ball is not necessary uponcompletion of the well fracturing process.

BACKGROUND

In well stimulation, the ability to perforate multiple zones in a singlewell and then fracture each zone independently, referred to as “zonefracturing”, has increased access to potential reserves. Many gas wellsare drilled with zone fracturing planned at the well's inception. Zonefracturing helps stimulate the well by creating conduits from theformation for the hydrocarbons to reach the well. A well drilled withplanned fracturing zones will be equipped with a string of piping belowthe cemented casing portion of the well. The string is segmented withpacking elements and frac plugs containing ball seats to isolate zones.A ball is dropped or pumped down the well and seats in the frac plug,thereby isolating pressure from above. Typically, a ball seat has anaxial opening of a select diameter. To the extent multiple frac plugsare disposed along a string, the diameter of these seats in therespective frac plugs becomes progressively smaller with the depth ofthe string. This permits a plurality of balls having a progressivelyincreasing diameter, to be dropped (or pumped), smallest to largestdiameter, down the well to isolate the various zones, starting from thetoe of the well and moving up. When the well stimulation in a particularzone is complete, pressure from within the formation should return theball utilized in a particular zone to the surface, carrying the ballupward in the flow of return fluids. In order to maximize the number ofzones and therefore the efficiency of the well, the diameter of theballs and the corresponding ball seats are very close in size from onezone to another. One-eighth inch increments are common. This means thata given ball has very little diametrical interference with the seatsupporting it since a ball with a diameter of one-eighth inch smallerthan the seat's axial opening must pass through that seat.

Conventional prior art frac balls are typically made of a non-metallicmaterial, such as reinforced epoxies and phenolics, that may be removedby milling in the event the balls become stuck. Such conventional priorart frac balls are made of materials that are designed to remain intactwhen exposed to hydraulic fracturing temperatures and pressures and arenot significantly dissolved or degraded by the hydrocarbons or othermedia present within the well. When one of these prior art balls doesnot return to the surface and prevents lower balls from purging, coiledtubing must be lowered into the wellbore to mill the stuck ball andremove it from the seat. In addition, smaller-sized prior art balls thatare not stuck in their seats still might not return to the surfacebecause the pressure differential across the ball due to the uprisingcurrent in the large diameter casing might not be significant enough toovercome gravity. Consequently, while such smaller-sized balls may notcompletely block a zone, they are still likely to impede production bypartially blocking the wellbore.

Dissolvable balls are sometimes used in a frac process know as perf andplug, where fracturing pressures are not as high. This fracturingprocess is used when preinstalled perforated casing string is notavailable and the zones are created through existing casing byperforating the casing to create formation flow paths therethrough.Specifically, using explosives, a relatively large number of small,radial holes are cut through the casing and cement. Typically, theseholes have an irregular shape with rough or jagged edges and varyingsizes due to the manner in which they are cut. Once the holes arecreated, the pumping process begins at the surface and the frac fluidfractures that zone through the newly cut radial holes. Upon completionof the zone, relatively small balls are carried in high quantities influid pumped from the surface in order to plug the perforated holes.These small balls must be malleable enough to block the irregularperforated holes in the casing. In this regard, these perf and plugballs typically have a high elongation and a low flexural modulus, thereason being that they must deform to plug the irregular shapes of thecasing perforations. These balls require a large ratio of ball diameterto seat diameter to withstand the pressure from fracturing the zoneabove. Perf and plug balls must remain intact under latent heat andpressure conditions for long periods of time and are often designed todissolve in water.

DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a ball of the present invention seated in a fracplug.

FIG. 2 illustrates a frac plug before the ball has become seated.

FIG. 3 shows a non-dissolving, prior art ball after becoming stuck inthe seat of a frac plug.

FIG. 4 illustrates perf and plug style balls of the prior art.

FIG. 5 illustrates a cut-away side view of a composite ball of thepresent invention in which a fabric is layered in parallel planes.

FIG. 6 illustrates a cut-away side view of a composite ball of thepresent invention in which multiple fabric layers are wrapped around acentral axis.

FIG. 7 illustrates a cut-away side view of a ball of the presentinvention in which a strengthening material is embedded in a basematerial.

DETAILED DESCRIPTION

The method and apparatus of the present invention provides a ball thatdisintegrates, dissolves, delaminates or otherwise experiences asignificant degradation of its physical properties over time in thepresence of hydrocarbons and formation heat. The term “disintegrate”with respect to the frac ball of the present invention is defined torefer generically to various processes by which the physical propertiesof the frac ball are significantly degraded such that the frac ball canno longer maintain a seal with respect to its corresponding ball seat,such processes including but not limited to disintegration, dissolutionand delamination.

The composition of the ball of the present invention permits it tomaintain its strength and shape for the time period required to fractureits assigned zone. In one embodiment, this time period is approximately10 hours.

The ball of the present invention is dropped down a wellbore onto a fracplug seat whereupon it is caused to seat in the frac plug as describedabove. Since the ball is immersed in frac fluid and dropped from thesurface, when it lands in the frac plug seat, the ball is atapproximately the same temperature as the frac fluid. Ambienttemperatures on the surface including heat generated from the pumps usedthe pump the frac fluid down hole, typically heat the frac fluid andconsequently the balls of the present invention to a temperature of nogreater than 150° F.

Frac fluid is then pumped into the frac zone in a conventional manner toinitiate formation fracturing. During the hydraulic fracturing process,the convective frac fluid from the surface pumped to fracture the zonealso serves as a coolant for the ball relative to latent hightemperatures. Since frac fluid must be continuously pumped to the ballto maintain the ball's position in the seat, the flow of frac fluid willkeep the ball at nearly the temperature of the frac fluid. Latent heatfrom the earth is transferred by convection to the ball and is in turntransferred and removed from the ball by convection to the frac fluid.In addition, the frac fluid displaces hydrocarbons within the wellminimizing hydrocarbon contact with the ball, thereby inhibitingdisintegration of the ball during the hydraulic fracturing process.

Once the frac zone is complete, a column of hydrocarbons, such as dieselfuel, is pumped onto the top or upper portion of the ball. This columnof fluid, sometimes referred to as a pad, effectively “soaks” theportion of the ball exposed to the frac zone and initiates thedisintegration of the ball. The next larger ball is then dropped orpumped into place on the frac plug immediately above the disintegratingball, and hydraulic fracturing procedures in the respective zone areinitiated. The newly seated ball functions to block frac fluid flow fromreaching the now disintegrating lower ball. Thus, the lower ball sits inits seat and continues to disintegrate in the presence of the pad whilethe zones above it are fractured. Without the relatively cool frac fluidreaching the lower ball, the lower ball's temperature will climb to thelatent temperature in the well bore. The latent temperature in the wellbore can reach, for example, in excess of 200° F., in excess of 220° F.,or in excess of 350° F. The latent formation heat and pressure, thehydrocarbon pad pumped from the top of the well, and to a lesser extent,hydrocarbons from the formation function to disintegrate the ball andinitially soften its exterior, stripping the ball of its rigidity andreducing the likelihood that it could become stuck in the seat. As timeelapses, the ball continues to disintegrate and soften towards the core.When the well begins to backflow, the currents effectively disintegratethe ball.

It should be noted that for several reasons, the ball will notdisintegrate in this controlled manner simply in the presence offormation hydrocarbons acting on the exposed lower surface of the ball,i.e., that portion of the ball that extends below the frac seat. First,the ball is intentionally cooled by the frac fluid pumped down the well.Second, the hydrocarbon pad that is pumped down the well is specificallyselected to yield a controlled disintegration of the ball. In oneembodiment, the pad is diesel fuel, which has a composition that rangesfrom approximately C₁₀H₂₀ to C₁₅H₂₈.

In addition to being subject to controlled disintegration in thepresence of hydrocarbons at temperatures in excess of 150° F. asdescribed above, and in contrast to the pert and plug balls describedabove, the disintegrating balls of the present invention are designedfor strength, rigidity and hardness sufficient to withstand the highpressure differentials required during well stimulation, which typicallyrange from about 1,000 pounds per square inch (psi) to about 10,000 psi.According to certain embodiments, the ball of the present invention isformed of a material or combination of materials having sufficientstrength, rigidity and hardness at a temperature of from about 150° F.to about 350° F., from about 150° F. to about 220° F. or from about 150°F. to about 200° F. to seat in the frac plug and then withstanddeformation under the high pressure ranging from about 1,000 psi toabout 10,000 psi associated with hydraulic fracturing processes. Forthis reason, according to some embodiments of the present invention theball is formed of a material having a Rockwell Hardness of M 75 orgreater.

According to one embodiment, the disintegrating ball of the presentinvention comprises polystyrene. Polystyrene is a relatively highstrength, rigid, high modulus resin that is not compatible withhydrocarbons and disintegrates in the presence of a hydrocarbon, such asdiesel, particularly at elevated temperatures, such as temperaturesabove 150° F. and/or pressures, such as 1,000 psi to 10,000 psi wherethe hydrocarbon acts as a solvent.

According to one embodiment, the ball of the present invention is madeof general purpose (GP) polystyrene, which may be substantially purewithout other significant additives. According to another embodiment,the ball of the present invention is made of high impact polystyrene(HIP) which may include additives. The following chain represents asuitable polystyrene for making the ball of the present invention:

With respect to degradation at latent temperatures in the wellbore, thedisintegrating ball of the present invention can be formed of any basematerial or combination of base materials that is sufficiently strongand rigid to support and not deform at a pressure of from 1,000 psi to10,000 psi at a temperature of less than 150° F., but that undergoes asignificant degradation of physical properties at temperatures in excessof 150° F., such that the disintegrating ball breaks apart into aplurality of particles, fragments or pieces that may easily be pumped tothe surface. For example, the base material may undergo a significantdegradation of physical properties at a temperature range of from about150° F. to about 350° F., from about 150° F. to about 220° F., or fromabout 150° F. to about 200° F. This can include polystyrene, asindicated above. Other base materials that have suitable strength andrigidity while also being subject to physical degradation at theappropriate temperatures, include thermosetting polymers, thermoplasticpolymers, elastomers and adhesives. Suitable thermosetting polymermaterials include phenolic resins, urea-formaldehyde resins, epoxyresins, melamine resins, crosslinked polyesters, polyimides,polyurethanes, cyanate esters, polycyanurates and melamine formaldehyde.Suitable thermoplastic polymer materials include acrylonitrile butadienestyrene, acrylates such as poly methyl methacrylate, polyoxymethylene,polyamides, polybutylene terephthalate, polyethylene terephthalate,polycarbonate, polyester, polyethylene, polyetheretherketone,polypropylene, polystyrene, polyvinylidene chloride andstyrene-acrylonitrile. Suitable elastomer materials include ethylenepropylene, polyisoprene, polybutadiene, chloroprene rubber, butylrubber, styrene-butadiene rubber and nitrile rubber. Suitable adhesivesinclude acrylates, methacrylates, and cyanoacrylate.

In certain embodiments, the disintegrating ball of the present inventionmay be formed of a material having a glass transition temperature (thetemperature at which the amorphous phase of a polymer is convertedbetween glassy and rubbery states) or a melting point temperature (thetemperature at which a material transitions from a solid state to aliquid state) in the appropriate temperature range, that is, in excessof 150° F. (65.5° C.), for example in the range of from about 150° F. toabout 350° F. (about 65.5° C. to about 176.7° C.), from about 150° F. toabout 220° F. (about 65.5° C. to about 104.4° C.), or from about 150° F.to about 200° F. (about 65.5° C. to about 93.3° C.). Such materials mayinclude, but are not limited to, the materials listed in Table 1 below.

TABLE 1 Example Polymeric Materials Glass Transition Melting PointRepeating Unit Temperature (T_(g)) (° C.) (T_(m)) (° C.) tent-Butylvinyl ether 88 250 3-Chlorostyrene 90 Cyclohexyl methacrylate 92Cyclohexyl vinyl ether 81 N,N-Dimethylacrylamide 89 4-Ethoxystyrene 86Ethylene terephthalate 72 265 Ethyl methacrylate 65 4-Fluorostyrene 952-Hydropropyl methacrylate 76 Indene 85 Isobornyl acrylate 94N-Isopropylacrylamide 85-130 Isopropyl methacrylate 81 Phenylenevinylene 80 380 Phenyl vinyl ketone 74 Styrene, atactic 100 Styrene,isotactic 100 240 Trimethylsilyl methacrylate 68 Vinyl alcohol 85 220Vinyl benzoate 71 Vinyl chloride 81 227 Vinylcyclohexanoate 76 Vinylpivalate 86

In another embodiment of the present invention, reinforcing material canbe added to the base material of the ball to increase the strength andrigidity of the ball so it can support higher pressures, such as fromabout 1,000 psi to about 10,000 psi when plugging a seat in a frac plug.Specifically, relatively high percentages of aramid, glass, carbon,boron, polyester, cotton and ceramic fibers or particles can elevate thepressure threshold the ball can sustain. Such fillers do not dissolve inhydrocarbons, but when the base material disintegrates, these fillersbecome inconsequential silt in the wellbore fluid. According to otherembodiments of the present invention, the ball can include compositefabric layers made of aramid, glass, carbon, boron, polyester, cotton orceramic fibers disposed within the base material. Such composite fabriclayers enable the ball to retain high strength at high pressures, suchas from about 1,000 psi to about 10,000 psi when plugging a seat in afrac plug.

According to certain embodiments, the ball of the present invention mayinclude one or more of (a) imbedded aramid, glass, carbon, boron,polyester, cotton or ceramic fibers, (b) one or more layers of fabricformed of aramid, glass, carbon, boron, polyester, cotton or ceramicfibers wrapped around the core of the ball, and (c) one or more layersof fabric formed of aramid, glass, carbon, boron, polyester, cotton orceramic fibers disposed in adjacent parallel planes.

According to certain embodiments, the ball of the present inventionincludes about 30 to about 90 percent by weight of the base material andabout 10 to about 70 percent by weight of fibers, particles or layers offabric. According to certain other embodiments, the ball of the presentinvention includes about 50 to about 70 percent by weight of the basematerial and about 30 to about 50 percent by weight of fibers, particlesor layers of fabric. In still other embodiments, the ball of the presentinvention includes about 60 percent by weight of the base material andabout 40 percent by weight of fibers, particles or layers of fabric.

Additionally, aluminum may be used to strengthen the disintegrating ballsince the corrosive environment in the well hole causes the aluminum todisintegrate as well.

FIG. 1 illustrates a polymeric, disintegratable frac ball 10 of thepresent invention in service. Frac ball 10 is seated on a frac plug seat12 which is sealably housed in a sleeve 14 carried in a tube 16 of apipe string 18. Sleeve 14 is slidable between a second position(illustrated in FIG. 1) and a first position (illustrated in FIG. 2).Those of ordinary skill in the art will appreciate that as fluid, suchas frac fluid, is pumped down the well as shown by the directional arrow20, a pressure differential between the upstream fluid 22 and thedownstream formation fluids 24 as applied across the ball 10 and seat 12urges sleeve 14 into the second position. In this second position,sleeve 14 abuts shoulder 26 of the tube 16. The tube 16 is provided witha plurality of radial apertures or holes 28 that serve as a conduit fromthe interior 30 of tube 16 to the formation 32, thereby permitting fracfluid pumped from the surface to infiltrate the annulus 34 between thepipe string 18 and the formation 32. Moreover, as will be appreciated inFIG. 2, when sleeve 14 is in the second position, apertures 28 are fullyopen to permit fluid flow therethrough. Packing element 36 is one ofmany packing elements that partition annulus 34 into zones. A secondpacking element (not shown) is disposed down stream of perforations 28so that the packing elements straddle the frac zone and seal the fraczone from the remainder of annulus 34.

In FIG. 2, sleeve 14 is shown in a first position, where a ball has notbeen dropped and the upstream fluid pressure from the frac pumps has notbeen applied to a seated ball to shift sleeve 14 to the second position.Radial apertures 28 are sealed from communication with interior 30.

In FIG. 3, a prior art ball 38 not capable of disintegrating isillustrated as distorted and wedged in seat 12 from the upstream pumppressure during the frac process. When the frac process is complete andthe upstream pump pressure is relieved, frac fluid and hydrocarbons withaccumulated pressure from the fracturing process and formation pressurepurge from the zones below. The wedged ball 38 restricts the return flowfrom the formations below, requiring expensive milling to remove theball.

FIG. 4 illustrates the prior art where pert and plug balls 40 showndisposed in radial apertures 42 formed in casing 44 and cement 46adjacent formation 32 by perforation procedures. Prior art balls 40 mustdistort in order to plug the perforated apertures 42 and typically havea large ball diameter to aperture diameter ratio. Fluid from inside thecasing 44 is normally passed through the perforated apertures 42 andinto the formation 32 while fracturing that zone. Typically, a largenumber of balls 40 are dropped into the stream from above with the hopeof blocking the apertures 42.

FIGS. 5 and 6 illustrate embodiments of a ball 10 of the presentinvention where fabric layers 46 partition material 48 for enhancedstrength. In FIG. 5, fabric layers 46 have a horizontal lay-up, while inFIG. 6, fabric layers 46 are wrapped around a center axis.

FIG. 7 illustrates an embodiment of ball 10 of the present invention inwhich reinforcing material, such as glass, ceramic or carbon fibers orparticles 50 is embedded in material 48.

While the ball 10 of the present invention has been described in theforegoing embodiments as including certain specific materials and thepad utilized to initiate degradation of the ball as diesel, those ofordinary skill in the art will appreciate that other ball material andpad solvent combinations may be utilized so long as they satisfy therequirements of the system described herein. In this regard, styrene isknown to have a solubility parameter of 8.7 δ(cal/cm³)^(1/2). Although apad of diesel is a preferred embodiment for a ball made of polystyreneas described herein, solvents with the same or similar solubilityparameters as polystyrene may also be satisfactory for the purposes ofthe present invention, such as for example, other hydrocarbons, oils,ketones, esters and inorganic acids. In one embodiment, hydrocarbons arepreferred because hydrocarbons are generally acceptable fluids undervarious regulatory standards for pumping into a wellbore and aretypically readily available at a well site, and are present naturally inthe well. In any event, materials with similar solubility parameters mayalso be satisfactory for ball 10 of the present invention. Finally, solong as the material used to form the ball of the present inventionsatisfies the other criteria set forth herein, particularly strength andrigidity, the ball may be formed of other polymeric or other materialswith a pad selected to have the same or similar solubility parameters asthe polymeric or other material of the ball.

Similarly, with respect to degradation at latent temperatures of thewellbore, so long as the material used to form the ball of the presentinvention satisfies the other criteria set forth herein, particularlystrength and rigidity, the ball may be formed of other polymericmaterials with a glass transition temperature and/or melting temperaturein the appropriate temperature range such that the materials undergosignificant physical degradation at temperatures in excess of 150° F.,such as from about 150° F. to about 350° F., from about 150° F. to about220° F., or from about 150° F. to about 200° F.

1. A fracturing system for a wellbore, said system comprising: a tubehaving a wall comprising an interior surface and an exterior surface; aball seat carried by the tube, the ball seat comprising an opening of afirst diameter; and a ball having a second diameter larger than thefirst diameter, the ball comprising a first material, wherein the firstmaterial is disintegrated by hydrocarbons.
 2. The system of claim 1,wherein the first material comprises polystyrene.
 3. The system of claim2, wherein the first material comprises general purpose polystyrene. 4.The system of claim 2, wherein the ball further comprises a secondmaterial, wherein the second material comprises fibers or particles ofat least one member selected from the group consisting of aramid, glass,carbon, boron, polyester, cotton and ceramics.
 5. The system of claim 2,wherein the ball further comprises a second material, wherein the secondmaterial comprises one or more layers of a composite fabric material,said composite fabric material comprising at least one member selectedfrom the group consisting of aramid, glass, carbon, boron, polyester,cotton and ceramic fibers.
 6. The system of claim 2, wherein the ballcomprises from about 30 percent to about 90 percent by weight of thefirst material.
 7. The system of claim 2, wherein the ball comprisesfrom about 50 percent to about 70 percent by weight of the firstmaterial.
 8. The system of claim 2, wherein the ball comprises about 60percent by weight of the first material.
 9. The system of claim 4,wherein the ball comprises about 60 percent by weight of the firstmaterial and about 40 percent by weight of the second material.
 10. Thesystem of claim 1, wherein the ball is seated in the opening of the ballseat so that a first portion of the ball is exposed above the openingand a second portion of the ball is exposed below the opening, thesystem further comprising a volume of hydrocarbon disposed in the tubeand in contact with the first portion of the ball.
 11. The system ofclaim 1, wherein the ball is seated in the opening of the ball seat andprevents fluid communication between a first portion of the tube abovethe ball and a second portion of the tube below the ball.
 12. The systemof claim 11, wherein the ball prevents fluid communication between thefirst and second portions of the tube at a pressure of up to about10,000 psi.
 13. The system of claim 1, wherein the ball seat comprises aflange disposed around the interior surface of the tube wall.
 14. Thesystem of claim 1, wherein the ball seat comprises a sleeve slidinglymounted within the tube between a first position and a second position.15. The system of claim 14, wherein the sleeve has an interior surfaceand an exterior surface, and further comprises a shoulder definedadjacent the interior surface.
 16. The system of claim 15, wherein theball seat further comprises a collar abutting the shoulder and in whichthe opening is defined.
 17. The system of claim 14, wherein the tubefurther comprises a plurality of apertures disposed in the tube wall,wherein the sleeve in the first position is adjacent the apertures so asto impede fluid flow therethrough.
 18. The system of claim 14, furthercomprising a plurality of ball seats, wherein each of the plurality ofball seats has an opening of a diameter different from those of theother ball seats; and a plurality of balls, each disposed to seat withinone of the openings of the ball seats, wherein each of the plurality ofballs has a diameter different from those of the other balls.
 19. Thesystem of claim 18, further comprising a pipe string in which the seatsare disposed, wherein the plurality of seats are arranged consecutivelyalong the pipe string from the seat with the largest diameter opening tothe seat with the smallest diameter opening.
 20. A fracturing system fora wellbore, said system comprising: a tube having a wall comprising aninterior surface and an exterior surface; a ball seat carried by thetube, the ball seat comprising an opening of a first diameter; and aball having a second diameter larger than the first diameter, the ballcomprising a first material, wherein the first material degrades at atemperature greater than 150° F.
 21. The system of claim 20, wherein thefirst material degrades at a temperature range of from about 150° F. toabout 350° F.
 22. The system of claim 20, wherein the first materialdegrades at a temperature range of from about 150° F. to about 220° F.23. The system of claim 20, wherein the first material degrades at atemperature range from about 150° F. to about 200° F.
 24. The system ofclaim 20, wherein the ball does not deform at a pressure of up to about10,000 psi.
 25. The system of claim 20, wherein the first material isselected from the group consisting of thermosetting polymers,thermoplastic polymers, elastomers and adhesives.
 26. The system ofclaim 20, wherein the first material comprises a thermosetting polymerselected from the group consisting of phenolic resins, urea-formaldehyderesins, epoxy resins, melamine resins, crosslinked polyesters,polyimides, polyurethanes, cyanate esters, polycyanurates and melamineformaldehyde.
 27. The system of claim 20, wherein the first materialcomprises a thermoplastic polymer selected from the group consisting ofacrylonitrile butadiene styrene, acrylates such as poly methylmethacrylate, polyoxymethylene, polyamides, polybutylene terephthalate,polyethylene terephthalate, polycarbonate, polyester, polyethylene,polyetheretherketone, polypropylene, polystyrene, polyvinylidenechloride and styrene-acrylonitrile.
 28. The system of claim 20, whereinthe first material comprises an elastomer selected from the groupconsisting of ethylene propylene, polyisoprene, polybutadiene,chloroprene rubber, butyl rubber, styrene-butadiene rubber and nitrilerubber.
 29. The system of claim 20, wherein the first material comprisesan adhesive selected from the group consisting of acrylates,methacrylates, and cyanoacrylate.
 30. The system of claim 20, whereinthe first material is selected from the group consisting of polystyrene,tert-butyl vinyl ether, 3-chlorostyrene, cyclohexyl methacrylate,cyclohexyl vinyl ether, N,N-dimethylacrylamide, 4-ethoxystyrene,ethylene terephthalate, ethyl methacrylate, 4-fluorostyrene,2-hydropropyl methacrylate, indene, isobornyl acrylate,N-isopropylacrylamide, isopropyl methacrylate, phenylene vinylene,phenyl vinyl ketone, atactic styrene, isotactic styrene, trimethylsilylmethacrylate, vinyl alcohol, vinyl benzoate, vinyl chloride,vinylcyclohexanoate and vinyl pivalate.
 31. The system of claim 20,wherein the ball further comprises a second material, wherein the secondmaterial comprises fibers or particles of at least one member selectedfrom the group consisting of aramid, glass, carbon, boron, polyester,cotton and ceramics.
 32. The system of claim 20, wherein the ballfurther comprises a second material, wherein the second materialcomprises one or more layers of a composite fabric material, saidcomposite fabric material comprising at least one member selected fromthe group consisting of aramid, glass, carbon, boron, polyester, cottonand ceramic fibers.
 33. A method for fracturing the formation around awellbore, the method comprising: deploying a pipe string into awellbore, the pipe string having perforations disposed in a wall of thepipe string and a ball seat positioned in the interior of the pipestring; setting packers above and below the perforations to seal theannulus formed between the pipe string and the formation; introducing adisintegratable ball comprised of a first material into the pipe string;seating the ball on the ball seat by applying a fluid pressure to theball, which fluid pressure is greater than the pressure of the wellbore,wherein the ball when seated, has an upstream portion and a downstreamportion; introducing fracturing fluids into the wellbore to initiatefracturing of the formation adjacent the perforations; cooling theupstream portion of the disintegratable ball during fracturing of theformation to inhibit disintegration of the ball; upon completion of thefracturing, introducing a hydrocarbon pad into the pipe string;contacting the upstream portion of the ball with the hydrocarbon pad topromote disintegration of the ball by the hydrocarbon pad; and allowingdisintegration of the ball to continue until the ball unseats from theball seat.
 34. The method of claim 33, wherein a pressure differentialacross the ball is maintained during fracturing.
 35. The method of claim34, wherein the upstream pressure applied to the ball is greater thanthe downstream pressure applied to the ball.
 36. The method of claim 35,wherein the upstream pressure is up to 10,000 psi.
 37. The method ofclaim 33, wherein a temperature differential across the ball ismaintained during fracturing.
 38. The method of claim 37, wherein theupstream temperature applied to the ball is less than the downstreamtemperature applied to the ball.
 39. The method of claim 33, wherein thefracturing fluid has a fluid temperature less than the temperature ofthe wellbore fluid;
 40. The method of claim 39, wherein the fracturingfluid is used to cool the ball during fracturing.
 41. The method ofclaim 33, wherein the hydrocarbon pad is diesel.
 42. The method of claim33, wherein the heat of the formation is used to accelerate degradation.43. The method of claim 33, wherein the first material comprises athermosetting polymer selected from the group consisting of phenolicresins, urea-formaldehyde resins, epoxy resins, melamine resins,crosslinked polyesters, polyimides, polyurethanes, cyanate esters,polycyanurates and melamine formaldehyde.
 44. The method of claim 33,wherein the first material comprises a thermoplastic polymer selectedfrom the group consisting of acrylonitrile butadiene styrene, acrylatessuch as poly methyl methacrylate, polyoxymethylene, polyamides,polybutylene terephthalate, polyethylene terephthalate, polycarbonate,polyester, polyethylene, polyetheretherketone, polypropylene,polystyrene, polyvinylidene chloride and styrene-acrylonitrile.
 45. Themethod of claim 33, wherein the first material comprises an elastomerselected from the group consisting of ethylene propylene, polyisoprene,polybutadiene, chloroprene rubber, butyl rubber, styrene-butadienerubber and nitrile rubber.
 46. The method of claim 33, wherein the firstmaterial comprises an adhesive selected from the group consisting ofacrylates, methacrylates, and cyanoacrylate.
 47. The method of claim 33,wherein the first material is selected from the group consisting ofpolystyrene, tent-butyl vinyl ether, 3-chlorostyrene, cyclohexylmethacrylate, cyclohexyl vinyl ether, N,N-dimethylacrylamide,4-ethoxystyrene, ethylene terephthalate, ethyl methacrylate,4-fluorostyrene, 2-hydropropyl methacrylate, indene, isobornyl acrylate,N-isopropylacrylamide, isopropyl methacrylate, phenylene vinylene,phenyl vinyl ketone, atactic styrene, isotactic styrene, trimethylsilylmethacrylate, vinyl alcohol, vinyl benzoate, vinyl chloride,vinylcyclohexanoate and vinyl pivalate.
 48. The method of claim 33,wherein the ball further comprises a second material, wherein the secondmaterial comprises fibers or particles of at least one member selectedfrom the group consisting of aramid, glass, carbon, boron, polyester,cotton and ceramics.
 49. The method of claim 33, wherein the ballfurther comprises a second material, wherein the second materialcomprises one or more layers of a composite fabric material, saidcomposite fabric material comprising at least one member selected fromthe group consisting of aramid, glass, carbon, boron, polyester, cottonand ceramic fibers.